10 markers cost $15.40. Which equation would help determine the cost of 9 markers?
Answer: There are several equations that could help determine the cost, each with a slightly different approach. If we let $x$ represent the cost of 9 markers, we have the following proportion: $\dfrac{x}{9}$ We have to pay $15.40 for 10 markers, and that can be written as a proportion: $\dfrac{\$15.40}{10}$ Since the price per marker stays the same, these two proportions are equivalent. $\dfrac{x}{9} = \dfrac{\$15.40}{10}$